It has been proposed that stretch wrap film be manufactured from polyvinylidene chloride, polyvinyl chloride, high pressure polyethylene, ethylene-vinyl acetate copolymer, polypropylene, linear low density polyethylene, polybutadiene, and other similar polymers. Those commonly used in the preparation of stretch wrap film are polyvinylidene chloride, polyvinyl chloride, high pressure polyethylene, and polybutadiene.
Since stretch wrap film is used in wrapping, protecting, storing, transporting, and displaying perishable foods, the following properties are desirable: it should be able to adhere to itself and yet be easily peeled off of the food: the stretch wrap film should have good heat sealing properties; it should be easily cut transversely with the sawtooth cutters used in packaging, and should not split longitudinally; the film should not contain impurities harmful to health; it needs good heat resistance and should be moisture proof, impervious to air, acid resistant, oil resistant, strong, extensible, and shrinkable; the stretch wrap film should also be transparent, drop resistant, and haze resistant; and it should not exhibit brittleness at low temperatures.
Polyvinylidene chloride stretch wrap film tends to wear in an unintended direction when cut with a sawtooth cutter; it shrinks to the breaking point when heated; and is brittle at low temperatures. Polyvinyl chloride film is similar to polyvinylidene chloride. In addition, the film tends to whiten in boiling water and contains a large amount of plasticizer, which can be considered an objectionable impurity. Further, the halogen present in both is also considered to be objectionable.
To overcome the deficiencies of polyvinylidene chloride and polyvinyl chloride films, high pressure polyethylene film was suggested as it does not contain halogen, but the film lacks the ability to adhere to itself and does not stretch. Ethylene-vinyl acetate copolymer film has good self-adherence, but poor mechanical strength and modulus. Polypropylene has good heat resistance, but is brittle at low temperatures; does not adhere to itself to any extent; and does not cut well with the sawtooth cutter. Linear low density polyethylene has the same cutting deficiency, and it is difficult to peel from itself, i.e., when provided as a rolled film. It does have good mechanical strength, however, when compared with high pressure polyethylene. Polybutadiene film has many desirable advantages, but its mechanical strength, e.g. tear strength, is poor, and it is expensive.